1. Field of the Invention
This invention relates in general to folding presses or like machines and has specific reference to a device for bending the tool holder of a machine of this type.
Hydraulic folding presses comprise a fixed beam and a movable beam, the fixed beam being supported at either end. The movable beam is actuated by hydraulic cylinders also disposed in most instances on either side.
These cylinders provide the power necessary for folding the sheet metal which, by reaction, causes the deformation of the two beams in the opposite direction. The distance between the two beams is therefore variable throughout the working period and consequently the folding angle becomes irregular in that it is greater in the central portion than at the ends of the beam assembly. Therefore, the sheet metal bending is more pronounced at its ends than in its central portion.
Various means have already been proposed with a view to impart a certain camber to the tool portions bearing against one of the beams. This bending should be adapted to each type of folding operation to be performed. It is subordinate on the one hand to the power requirements per unit length of sheet metal to be folded, and on the other hand to the length of the workpiece.
Therefore, the operator should be in a position to adjust this tool bending as a function of these two requirements.
2. The Prior Art
Several arrangements have been proposed for solving this problem. Inter alia, the French Pat. Nos. 1,132,633, 1,362,471 and 1,539,817 provide an arrangement in which hydraulic cylinders are mounted in the central portion of the press, whereby the beam distortion curves have the same direction and magnitude, thus ensuring a regular and accurate folding of the sheet metal.
Another French Pat. No. 2,347,992 discloses a folding press in which one of the beams comprises two sections, namely a first section supported or actuated at one end and another section, or bolster, supporting the corresponding tool; these two sections are connected by means of one or two common pins disposed symmetrically in relation to the transverse median plane and relatively close to this plane.
The two-section beam may comprise prestress means at either end for causing initially the operative section of this beam, i.e. the working tool supporting section, to undergo a distortion of same direction and substantially parallel to the deformation produced in the other beam when subjected to the folding stress.
With this arrangement, the deformation curves obtained for the two operative edges of the fixed and movable beams are as close as possible to each other.
Another French Pat. No. 1,420,380 describes a set of shims or liners disposed between one of the beams and the corresponding folding tool member; the thickness of these shims varies in the longitudinal direction of the tool and is adjustable separately in order to provide the desired bending curve. A further French Pat. No. 2,078,874 discloses the use of a single shim in the form of a tapered elongated bar movable laterally by means of separately adjustable set screws.
Another solution is contemplated in the German Pat. No. 1,752,346 disclosing a bending device comprising a set of wedges or shims fastened to a support extending along the beam and reacting against tapered surfaces, all these wedges having a tapered face in the longitudinal direction of the tool and being adjustable by means of a common mechanical device disposed at one end of the row of wedges. Other known constructions comprise hydraulic means for bending the tool; thus, the French Pat. No. 2,200,064 discloses a press in which one of the tools is supported by several vertical hydraulic cylinders disposed at spaced intervals along the press and interconnected by a closed-loop hydraulic system.
On the whole, these known bending devices are relatively complicated and therefore expensive.